Simultaneous monitoring of head-to-cervix forces, intrauterine pressure and cervical dilatation during labour

Fetal defenses against intrapartum head compression-implications for intrapartum decelerations and hypoxic-ischemic injury

Uterine contractions during labor and engagement of the fetus in the birth canal can compress the fetal head. Its impact on the fetus is unclear and still controversial. In this integrative physiological review, we highlight evidence that decelerations are uncommonly associated with fetal head compression. Next, the fetus has an impressive ability to adapt to increased intracranial pressure through activation of the intracranial baroreflex, such that fetal cerebral perfusion is well-maintained during labor, except in the setting of prolonged systemic hypoxemia leading to secondary cardiovascular compromise. Thus, when it occurs, fetal head compression is not necessarily benign but does not seem to be a common contributor to intrapartum decelerations. Finally, the intracranial baroreflex and the peripheral chemoreflex (the response to acute hypoxemia) have overlapping efferent effects. We propose the hypothesis that these reflexes may work synergistically to promote fetal adaptation to labor.

Forces Involved with Labor and Delivery-A Biomechanical Perspective

Childbirth is a primarily biomechanical process of physiology, and one that engineers have recently begun to address in a broader fashion. Computational models are being developed to address the biomechanical effects of parturition on both maternal and fetal tissues. Experimental research is being conducted to understand how maternal tissues adapt to intrauterine forces near the onset of labor. All of this research requires an understanding of the forces that are developed through maternal efforts-both uterine contractions and semi-voluntary pushing-and that can be applied by the clinician to assist with the delivery. This work reviews the current state of knowledge regarding forces of labor and delivery, with a focus on macro-level biomechanics.

An empirical model for educational simulation of cervical dilation in first-stage labor

Background

Several models for educational simulation of labor and delivery were published in the literature and incorporated into a commercially available training simulator (CAE Healthcare Lucina). However, the engine of this simulator does not include a model for the clinically relevant indicators: uterine contraction amplitude and frequency, and cervical dilation. In this paper, such a model is presented for the primigravida in normal labor.

Methods

The conceptual and mathematical models represent oxytocin release by the hypothalamus, oxytocin pharmacokinetics, and oxytocin effect on uterine contractions, cervical dilation, and (positive) feedback from cervical dilation to oxytocin release by the hypothalamus.

Results

Simulation results for cervical dilation are presented, together with target data for a normal primigravida. Corresponding oxytocin concentrations and amplitude and frequency of uterine contractions are also presented.

Conclusion

An original empirical model for educational simulation of oxytocin concentration, uterine contractions, and cervical dilation in first-stage labor is presented. Simulation results for cervical dilation match target data for a normal patient. The model forms a basis for taking into account more independent variables and patient profiles and can thereby considerably expand the range of training scenarios that can be simulated.

A Systematic Review of Intrapartum Fetal Head Compression: What Is the Impact on the Fetal Brain?

Objective During labor the fetal head is subjected to pressure related to uterine contractions and maternal pushing. Here we systematically review what is known about fetal head compression and its effects on fetal intracranial pressure, oxygenation, blood flow and cerebral function, and the plausibility that it might cause isolated fetal brain injury. Study Design Systematic review of intrapartum fetal head compression and fetal brain injury in accordance with the MOOSE methodology. The PubMed database was searched using a combination of the terms "fetal," "head," "cranial," "extracranial," "pressure," and "compression." Additional references were obtained using multiple strategies. Results were evaluated, and relevant studies encompassing animal and human data using several approaches are summarized in this review. Results Studies support a significant increase in fetal extracranial pressure with contractions and pushing. However, available data do not support a concomitant significant relative increase in intracranial pressure, a reduction in cerebral circulation or oxygenation, or an impact on cerebral function. Conclusion A review of the literature indicates that fetal intracranial pressure is well protected from extracranial forces. Available data do not support intrapartum fetal extracranial pressure as a cause of fetal brain injury. Precis The fetal brain is relatively unaffected by intrapartum fetal head compression.

Association of First-Trimester Echogenicity of the Puborectalis Muscle With Mode of Delivery

OBJECTIVE

To evaluate the association between mean echogenicity of the puborectalis muscle, measured using transperineal ultrasonography, in women during their first pregnancy and the subsequent mode of delivery.

METHODS

This is a secondary analysis of a prospective observational study on the association between stress urinary incontinence and levator muscle avulsion after delivery of a first pregnancy. In this study, 280 nulliparous women with singleton pregnancies were examined with transperineal ultrasound examination at 12 and 36 weeks of gestation. Patients were recruited from an obstetrics practice associated with the university medical center in Utrecht, the Netherlands. Mean echogenicity of the puborectalis muscle values were measured at rest, in pelvic floor muscle contraction, and during the Valsalva maneuver. The subsequent mode of delivery was classified into five categories: spontaneous vaginal delivery, instrumental vaginal delivery, elective cesarean delivery, cesarean delivery resulting from nonreassuring fetal status, and cesarean delivery resulting from failure to progress. Mean echogenicity of the puborectalis muscle values according to mode of delivery were compared by analysis of variance and Tukey's post hoc test.

RESULTS

Of the 254 women included, 157 had spontaneous vaginal delivery, 47 underwent cesarean delivery (11 elective, 36 emergency), and 45 had vacuum operative vaginal delivery; in five patient files, the mode of delivery was not recorded. Of the analyzed women, those who delivered by cesarean because of failure to progress had a significantly lower mean echogenicity of the puborectalis muscle in pelvic floor contraction at 12 weeks of gestation (mean echogenicity of 116±14) than women who had spontaneous vaginal delivery (132±21; Tukey's post hoc test, P=.03), instrumental vaginal delivery (138±21; P=.004), and cesarean delivery resulting from nonreassuring fetal status (139±20; P=.02).

CONCLUSION

Lower mean echogenicity of the puborectalis muscle values in pelvic floor contraction during the first pregnancy at 12 weeks of gestation is associated with subsequent cesarean delivery as a result of failure to progress.

[Increased prevalence of congenital dacryostenosis following cesarean section]

BACKGROUND

Congenital nasolacrimal duct obstruction (dacryostenosis) with a persisting membrane at Hasner's valve is the most common cause of persistent tear and ocular discharge in infants.

PURPOSE

To evaluate whether there is an association between congenital dacryostenosis and delivery via cesarean section.

MATERIAL AND METHODS

In a prospective study we examined 107 children (mean age 9.2 ± 7.1 months) with congenital dacryostenosis. We evaluated data about the mode of delivery (vaginal delivery versus cesarean section) and gestational age at the time of birth. Within the first 8 months of life children were treated by probing using local anesthesia, whereas older children were treated using general anesthesia. After the age of 11 months treatment included nasolacrimal duct intubation with a bicanalicular stent. Statistical analyses were performed using binomial tests, Fisher's exact test and the t-test.

RESULTS

In this study 51 children delivered by cesarean section were compared with 56 children delivered by spontaneous vaginal delivery. A total of 44 age-matched pairs from both groups were evaluated in order to eliminate confounding factors due to gestational age at delivery. Based on the published rate of cesarean sections from the same region of the State of Hesse between 2002-2004 we observed a statistically significant association between congenital dacryostenosis and delivery by cesarean section among the 88 age-matched patients (P = 0.009). Moreover, subgroup analysis revealed a significant association between congenital dacryostenosis and delivery by primary cesarean section (P = 0.00004). The prevalence of surgical treatment was not statistically different between both groups based on the mode of delivery (P = 0.8).

CONCLUSION

Our results suggest that delivery via cesarean section is associated with a significantly higher prevalence of congenital dacryostenosis.

Automatic evaluation of progression angle and fetal head station through intrapartum echographic monitoring

Labor progression is routinely assessed through transvaginal digital inspections, meaning that the clinical decisions taken during the most delicate phase of pregnancy are subjective and scarcely supported by technological devices. In response to such inadequacies, we combined intrapartum echographic acquisitions with advanced tracking algorithms in a new method for noninvasive, quantitative, and automatic monitoring of labor. Aim of this work is the preliminary clinical validation and accuracy evaluation of our automatic algorithm in assessing progression angle (PA) and fetal head station (FHS). A cohort of 10 parturients underwent conventional labor management, with additional translabial echographic examinations after each uterine contraction. PA and FHS were evaluated by our automatic algorithm on the acquired images. Additionally, an experienced clinical sonographer, blinded regarding the algorithm results, quantified on the same acquisitions of the two parameters through manual contouring, which were considered as the standard reference in the evaluation of automatic algorithm and routine method accuracies. The automatic algorithm (mean error ± 2SD) provided a global accuracy of 0.9 ± 4.0 mm for FHS and 4° ± 9° for PA, which is far above the diagnostic ability shown by the routine method, and therefore it resulted in a reliable method for earlier identification of abnormal labor patterns in support of clinical decisions.

Vulnerability of continence structures to injury by simulated childbirth

The goal of this study was to examine acute morphological changes, edema, muscle damage, inflammation, and hypoxia in urethral and vaginal tissues with increasing duration of vaginal distension (VD) in a rat model. Twenty-nine virgin Sprague-Dawley rats underwent VD under anesthesia with the use of a modified Foley catheter inserted into the vagina and filled with saline for 0, 1, 4, or 6 h. Control animals were anesthetized for 4 h without catheter placement. Urogenital organs were harvested after intracardiac perfusion of fixative. Tissues were embedded, sectioned, and stained with Masson's trichrome or hematoxylin and eosin stains. Regions of hypoxia were measured by hypoxyprobe-1 immunohistochemistry. Within 1 h of VD, the urethra became vertically elongated and displaced anteriorly. Edema was most prominent in the external urethral sphincter (EUS) and urethral/vaginal septum within 4 h of VD, while muscle disruption and fragmentation of the EUS occurred after 6 h. Inflammatory damage was characterized by the presence of polymorphonuclear leukocytes in vessels and tissues after 4 h of VD, with the greatest degree of infiltration occurring in the EUS. Hypoxia localized mostly to the vaginal lamina propria, urethral smooth muscle, and EUS within 4 h of VD. Increasing duration of VD caused progressively greater tissue edema, muscle damage, and morphological changes in the urethra and vagina. The EUS underwent the greatest insult, demonstrating its vulnerability to childbirth injury.

The need for a new outlook on labor monitoring

Fetal heart rate monitors, including the newer pulse-oximetry and STAN monitors, are designed to detect fetal distress that affects less than 1% of women in labor. Non-progressive labor is a much more common disorder than fetal distress, with approximately 50% of women in labor requiring oxytocin. Current technology assessing labor progress is subjective and inaccurate. There is a need for objective and accurate technology to measure labor progress and the effect it may have on managing labor and, specifically, non-progressive labor.

Continuous monitoring of cervical dilatation and fetal head station during labor

An ultrasound-based computerized system was developed for monitoring cervix dilatation and fetal head station during labor. The system was designed to provide continuous and accurate assessment of the progression of labor. The computerized labor-monitor (CLM) was tested in the laboratory and was studied in over 95 women during labor. The laboratory test showed that the mean error of measurement is 0.1 mm with standard deviation of 1.14 mm. In the clinical experiments, safety of the various system components was demonstrated and partograms were compared to manual measurements. The systematic error of the fetal head station measurement is estimated as 10-20%, depending on patient's anatomy. In addition, the clinical tests indicated that measurements of the changes of both cervix dilatation and fetal head station are feasible. The CLM is expected to change patient management in the labor room. It will enable timely recognition of abnormal labor patterns such as dysfunctional and precipitous labor. Continuous accurate data will allow earlier diagnosis and intervention that is very likely to improve both mother's and baby's clinical outcome.

Sonographic assessment of the cervix before, during and after a uterine contraction is effective in predicting the course of labor

OBJECTIVE

To investigate whether the degree of change in cervical length during a uterine contraction is predictive of subsequent progression of labor.

METHODS

The subjects were 73 uncomplicated parturient women at term. We observed the cervix before, during and after a uterine contraction by transvaginal ultrasound in the first stage of labor and determined the degree of cervical shortening during the contraction relative to the cervical length before contraction. We related the degree of cervical shortening to labor patterns at the time of the ultrasound examination, which were retrospectively determined by reviewing the partogram.

RESULTS

The cervix was shortened in length by about 50% on average during a uterine contraction in the normal course of labor. The degree of cervical shortening was significantly greater in the normal latent and active phases than it was in the prolonged latent phase, protracted active phase and false labor, whereas there were no differences between the former two phases nor between the latter three phases. Nulliparous and parous women exhibited almost the same degree of shortening in the normal latent and active phases.

CONCLUSIONS

Real-time ultrasound observation of the cervix during uterine contraction could help differentiate inefficient uterine contractions from normal ones and thus predict the subsequent course of labor.

Cervical dilatation related to uterine electromyographic activity and endocrinological changes during prostaglandin F(2alpha)-induced parturition in cows

The temporal relationship between changes in cervical dilatation, uterine electromyographic (EMG) activity, and maternal plasma concentrations of estradiol 17beta (E(2)), progesterone (P(4)), and 13,14-dihydro-15-keto-prostaglandin-F(2alpha) (PGFM), was investigated in six parturient cows. Calving was induced with a single injection of a synthetic analogue of prostaglandin F(2alpha) (PG) on Day 274 of gestation. Cervical dilatation was measured continuously by measuring the transit time between two implanted ultrasound crystals while at the same time uterine EMG activity was measured through two silver electrodes sutured on the myometrial surface until the expulsive stage of calving had been reached. In blood samples collected at 4-h intervals, starting at the moment of PG injection, the mean plasma E(2) concentration gradually increased and was significantly elevated at 28 h after PG injection. At 4 h after PG treatment, the mean P(4) concentration had dropped significantly and continued to decrease until a value of around 1 ng/ml was reached, where it stayed until the onset of expulsion. Mean plasma PGFM concentrations increased steadily after PG injection, reaching significantly elevated concentrations at 20 h after treatment. In the five cows that delivered calves in anterior positions, uterine EMG activity, expressed as root mean square (RMS in microV), started to increase at a mean interval (+/- SD) of 13.1 +/- 3.7 h following PG treatment. The increase in EMG activity was significantly correlated with changes in plasma PGFM concentrations. In these cows, dilatation of the caudal cervix started after a mean (+/- SD) interval of 28.5 +/- 1.5 h following PG treatment and dilatation progressed at a mean (+/- SD) rate of 2.25 +/- 0.24 cm/h. In one cow with a calf in the posterior position, uterine EMG activity and dilatation started at 15.8 h and 31.8 h, respectively, after induction of calving. We conclude that a predictable sequence of physiological changes occurs around induction of calving, which allows specific timing of future studies on cellular and biochemical changes within the cervix during parturition.

Ultrasonic cervimetry to study the dilatation of the caudal cervix of the cow at parturition

The objective of this study was to investigate the temporal changes in dilatation of the caudal cervix during induced calvings (n = 5). We used ultrasound cervimetry, allowing the continuous recording of the distance between a transmitting and receiving ultrasound crystal, which were implanted opposite to each other on the caudal rim of the cervix. We started recording between 19 and 21 h after injecting a prostaglandin analogue (PG) on day 272 of gestation. A fluid-filled catheter had been introduced transcervically between the fetal membranes and the uterine wall for measurements of intra-uterine pressure (IUP). While the characteristics of calving varied widely between the five animals, it appeared possible to divide the process of dilatation into four phases. During the latent phase, which lasted until 25-43 h after PG, no net gain in dilatation occurred. We found an acceleration phase (4.3-6.8 h), in which the dilatation rate speeds up (0.49-0.84 cm/h) in three of the cows. During the phase of maximum slope (lasting 0.5-4.8 h), we measured an even higher rate (1.47-8.48 cm/h), decreasing again during the deceleration phase (rate 0.24-2.28 cm/h) in four cows. The quality of the IUP measurements precluded us from continuously investigating the relationship between cervical dilatation and uterine contractions. However, short term simultaneous recordings revealed that the cervical opening changed momentarily in the absence of IUP during the latent phase, while during the phase of maximum slope, temporary changes of dilatation coincided with uterine contractions. We concluded that the method of ultrasound cervimetry used in this study provides a valuable way to study the process of cervical dilatation in parturient cows in vivo.

Fetal head moulding: finite element analysis of a fetal skull subjected to uterine pressures during the first stage of labour

Fetal head moulding is a phenomenon which may contribute to satisfactory progress during delivery as it allows the fetal head to accommodate to the geometry of the passage. In contrast, excessive head moulding may result in cranial birth injuries and thus affect the infant shortly or even long after birth. One group of researchers in the past investigated the biomechanics of fetal head moulding from an engineering point of view and limited themselves to a static, linear model of the parietal bones. In this paper, we present a non-linear model of the deformation of a complete fetal skull, when subjected to pressures exerted by the cervix, during the first stage of labour. The design of the model involves four main steps: shape recovery of the fetal skull, the generation of a valid and compatible mesh for finite element analysis (FEA), the specification of a physical model and the analysis of deformation. Results of the analysis show good agreement with those obtained from clinical experiments on the quantitative assessment of fetal head moulding. The model also displays shapes after moulding which have been reported in previous studies and which are generally known in the obstetric and paediatric communities.